Olefin/alkyl-acrylate-ester copolymers, which may contain two or more different comonomers, are important items of commerce, being potentially useful as oil-resistant elastomers, hot melt adhesives, in-contact adhesives, and other products. Copolymers in which ethylene is the primary or sole olefin are commercially well known.
It is often desirable to readily crosslink (or cure) such polymers, particularly when these polymers are to be used as elastomers. For this reason, the polymer may include certain monomers (repeat units) which allow the polymer to be easily cured. These monomers, however, may sometimes make the polymerization more difficult. It would, therefore, be desirable to make olefin/acrylate-ester copolymers that are easily polymerized and that can be readily converted to copolymers that are easily cured.
The presence of allylic hydrogens (i.e., of the type C.dbd.C--C--H) in a polymer may indicate that the polymer is readily curable, for example, by sulfur or peroxides. The process described herein can produce polymers with such groupings by the at least partial transesterification of an olefin/alkyl-acrylate copolymer with an alkenyl alcohol in the presence of an alkali metal alkoxide catalyst. These catalysts are surprisingly active, allowing rapid reaction at relatively low temperatures. This results in relatively little degradation of the polymer during the process.
DE 37 15 027 A1 discloses the bulk transesterification of ethylene/alkyl acrylate ester copolymers with unsaturated fatty alcohols with an average of 12 to 20 carbon atoms and tricyclodecanol utilizing acid or tin catalysts in the temperature range of 20.degree. to 230.degree. C. for 5 to 8 hours.
U.S. Pat. No. 3,418,395 describes the transesterification of ethylene/acrylic-ester copolymers with alcohols containing tertiary amine groups. Various catalysts, including alkoxides, are mentioned. Alkoxides are not actually used in any of the examples.
PCT Patent Application 90/10654 describes the crosslinking of an ethylene/unsaturated-ester copolymer (acrylate-ester copolymers) by transesterification with a polyol, optionally in the presence of a catalyst. Only tin containing catalysts are used in the examples.
G. Hu et al., Polymer, vol. 35, p. 3082-3090 (1994) describe the transesterification of an ethylene/methyl-acrylate copolymer with 3-phenyl-1-propanol in the presence of various catalysts. Sodium methoxide is shown to be a poor catalyst with low activity.